Legionella pneumophila is a ubiquitous bacterium associated with fresh water. This microorganism can cause a potentially fatal pneumonia, i.e., Legionnaire's Disease, pneumonia, Pontiac fever, if inhaled; and thus is a serious problem for owners, operators, and treaters of domestic water systems, including operators of public facilities which provide water, such as hotels and restaurants, etc. While outbreaks of L. pneumophila infection associated with cooling water systems are rarer than outbreaks linked to domestic water systems, such as fountains and HVAC-related components, the ability of cooling towers to spread water droplets contaminated with L. pneumophila can cause an outbreak that covers a wide geographical area.
To provide guidance to owners, operators, and treaters of cooling systems various guidelines, codes of practices, and regulations have been put into place globally to detect and/or control the spread of Legionella in water sources. In North America, there are two guidelines written by industry groups that are soon to be finalized—the ASHRAE 188P and the CTI STD-159 standard. In addition, OSHA has recommended action levels for remediation and treatment based on counts of Legionella found in either domestic or industrial water systems.
The ability to identify and/or quantitatively identify Legionella from a mixed microbial population in a water source is critical to determine the potential for infections and to determine if the current treatment protocol is effective at either preventing or remediating Legionella in any water system. The US CDC has recommended a culture-based test approach that leverages the acid-tolerance of Legionella, a distinctive colony morphology, inherent resistance to the antibiotics glycine, vancomycin, polymixin B and cyclohexamide and the absolute requirements of addition iron and L-cysteine in growth media to successfully enrich Legionella bacteria from a mixed culture. However, Legionella is also a relatively slow-growing organism that requires 2-10 days under optimal growth conditions to appear on growth media. Given the complex media requirements to successfully isolate Legionella and the relatively lengthy incubation time needed for each growth step, this method for detecting Legionella is not optimal.
Other detection technologies take advantage of unique Legionella outer membrane proteins. A latex agglutination method by Oxoid Ltd, United Kingdom is a tool for confirming that a Legionella colony is in fact L. pneumophila SG1, the strain most linked to Legionella outbreaks. Other methods such as Biotica's LEGIPID™ test and Hydrosense's colorimetric antibody test, which has been marketed by Nalco as the Fastpath Duo System, are relatively rapid antibody-based detection methods for Legionella in water. For a direct visualization of Legionella in water there are fluorescent antibodies that delineate Legionella by serogroup 1 and 2-14/15/16 that can be used with a fluorescent microscope. A limitation of these methodologies and devices is that they require proteins to detect Legionella. As proteins can exist in water after cell death, these methods can result in false positive detections.